In order to effectively improve the coverage and the communication capacity of a system, the 3rd Generation Partnership Project (3GPP) is currently researching deployment of a small cell (or a micro eNB) in the LTE-A system. Compared with a macro eNB (or a macro cell), a radio frequency transmission power of the small cell is smaller than that of the macro eNB, thus, the coverage of the small cell is smaller than that of the macro eNB. One or more micro eNBs are often deployed in a specific region within the coverage of a macro eNB depending on different terrain conditions and customer requirements, such that the coverage of the network is enhanced and radio resources are reused, and the capacity of the system is increased.
A user may keep in a radio resource control (RRC) connection status with a macro cell and a small cell when positioning within the coverage of both the macro cell and the small cell, i.e., the macro cell and the small cell can both serve the user, and the user can maintain two physical communication links with respect to the macro cell and the small cell. In a case that the both eNBs serve the user, an eNB acts as a master eNB (MeNB), and the other eNB acts as a secondary eNB (SeNB). Typically, the MeNB is configured to facilitate the user to control and manage related information, and the SeNB is mainly configured to provide related radio resources to the UE. This network architecture is often referred to as a dual connection mechanism. With this dual connection mechanism, communication rates of an uplink channel and a downlink channel and the communication capacity of the system are enhanced effectively, further, it also has the advantages of signalling optimization and enhanced mobile robustness. A kind of typical dual connection network architecture is shown in FIG. 1, in which, a terminal can receive signals from a macro cell and a small cell at the same time, and information can be transmitted between the macro cell and the small cell.
In the conventional technologies, reference is made to FIG. 2, in case of using the dual connection mechanism, a control plane of a user is managed by an MeNB, and an SeNB is responsible for providing radio resources of a user plane, in which, a dotted line refers to information transmission of the user plane, a solid line refers to information transmission of the control plane.
In the dual connection mechanism, the related information about the control plane of the user is controlled and managed by the MeNB. Two transmission mechanisms are provided for data of the user plane. The two transmission mechanisms are explained hereinafter taking an example of transmission of downlink data sent from a network to a UE.
A transmission mechanism is that, data from a user is separated at a service gateway (SGW) node in a core network, a portion of the data is transmitted to a UE via an MeNB, and the other portion of the data is transmitted to an SeNB through the SGW and then transmitted to the UE, and this data transmission mechanism is referred to as data distribution for the core network.
The other transmission mechanism is referred to as data distribution for a wireless network, in which, data from a user is first sent to an MeNB through an SGW, and a portion of the data is sent by the MeNB to an SeNB, and then is sent by the SeNB to a UE, and the other portion of the data is directly sent by the MeNB to the UE.
In a mechanism of the data distribution for the wireless network, bearers are divided between an MeNB and an SeNB, as shown in FIG. 3, in a downlink direction in which data is sent to a UE via a network, data on a bearer#2 is passed through an interface S1 and processed via a Packet Data Convergence Protocol (PDCP) layer of the MeNB, i.e., encryption/integrity protection and header compression are performed on the data, and then a portion of the data is processed via a Radio Link Control/Media Access Control (RLC/MAC) of the MeNB and transmitted to the UE, and the other portion of the data is passed through an interface Xn and processed via RLC/MAC of the SeNB and transmitted to the UE, i.e., this data is distributed to the SeNB and transmitted to the UE. In FIG. 3, data on a bearer#1 is not distributed via the SeNB, but totally processed via the MeNB and sent to the UE.
Further, in an uplink direction of data, i.e., in a direction in which the data is sent to an eNB from a UE, the uplink data is separated between the MeNB and the SeNB when the mechanism of the data distribution is performed on the uplink data, as shown in FIG. 4, in the uplink direction, data on a bearer#2 is passed through an interface UE IP App and processed via the PDCP layer of the MeNB, a portion of the data is processed via an RLC/MAC of the UE and transmitted to the MeNB, and the other portion of the data is processed via another RLC/MAC of the UE and transmitted to the SeNB. In FIG. 4, data on a bearer#1 is not distributed via the SeNB, and is totally processed via a PDCP/RLC/MAC of the UE and sent to the MeNB.
In the conventional technologies, when a UE intends to send data to an eNB, the UE may first report the eNB the size of buffer data, and the eNB may therefore determine and allocate a proper radio resources for the UE based on the size of buffer data. The procedure of reporting the size of buffer data by the UE to the eNB is referred to as Buffer Status Reporting (BSR).
In a case that the UE reports its own BSR, the UE should report a total size of data to be transmitted on each bearer, data transmission of which is uninterrupted, and the UE may report a size of data on bearers, data transmission of which have been interrupted.
In a case that the UE reports its own BSR, a size of data to be transmitted is calculated as a total size of data to be transmitted on a PDCP layer and an RLC layer included in all of the logic channels of a specific Logical Channel Group (LCG). Specifically, for a size of data to be transmitted on the PDCP layer, the UE should take into account a Protocol Data Unit (PDU) of the PDCP and a Service Data Unit (SDU) and a PDU being not processed by the RLC. Moreover, for a size of data to be transmitted on the RLC layer, the UE should take into account an RLC SDU of the RLC layer or segments of the SDU being not encapsulated into an RLC PDU, and a PDU of the RLC or data blocks to be re-transmitted. When reporting the BSR, the UE indicates a sequence number of the LCG and a corresponding total size of data to be transmitted (Buffer Size), wherein the buffer size may be extended. The general format of the buffer size is shown in FIG. 5, the LCG ID is 2 bits long, and the buffer size is 6 bits long.
When both of the MeNB and the SeNB serve the UE at the same time, the UE should report its data buffer size to both of the MeNB and the SeNB. If uplink data from the UE is transmitted to the MeNB and the SeNB using a distribution mechanism, an error may occur to the BSR from the UE. When uplink bearers of the UE are distributed, i.e., a portion of the uplink data is transmitted to the MeNB, and the rest is transmitted to the SeNB, when the UE reports a BSR for each eNB, the UE may calculate a total size of data to be transmitted on its own LCG and report it to all eNBs, and then the total size of data to be transmitted is received by each eNB. However, in fact, the UE may perform a distribution operation on the uplink data, which causes that a portion of the uplink data is transmitted to a certain eNB, rather than whole of the uplink data. It means that the BSR received by the eNBs from the UE is not accurate. The eNB may allocate excessive radio resources for the UE to transmit data if inaccurate BSR is used by the eNB, thereby radio resources are wasted, and the performance of the system is reduced.
With respect to the above problems, no mechanism is provided to solve the above problems currently. Therefore, technical problems to be solved are that, in a case that both the MeNB and the SeNB provide a dual connection service for the UE, the UE should process a BSR reported by the MeNB and the SeNB when performing distribution transmission on uplink data, such that radio resources are better allocated by the eNBs.